The present invention relates to liquid dispensing apparatus and pertains particularly to an improved infusion apparatus for delivering intravenous drugs at a controlled rate to a patient.
It is often necessary to intravenously supply patients with pharmaceutically active liquids over a long period of time at a controlled rate. In many instances it is desirable that this be accomplished while the patient is in an ambulatory state. A few devices have been developed in the past for accomplishing this purpose.
The prior art devices typically comprise an elastic bladder forming a liquid container mounted in an elongated cylindrical housing, and having a flow control valve or device and tubing for supply of the liquid to the patient. The elastic walls of the bladder expand along the walls of the cylindrical housing when filled with the liquid, and provide the pressure for expelling the liquid. These prior art devices are typically filled by hand by means of a syringe which often requires an inordinate amount of force.
Another drawback to these prior art devices is that the bladder is forced to expand into an unnatural elongated configuration along the housing walls as the container is filled. As a result of this unnatural configuration, the pressure of the bladder varies widely with the volume of liquid therein. Therefore, they do not have a reasonably stable pressure and flow rate over the infusion period.
Most of such devices either have a flow rate that decreases with pressure, which decreases with volume, or one that remains roughly constant until the end where it surges. Attempts have been made to control pressure and flow rates by means of complicated and expensive flow control valves and devices. Other approaches have utilized exotic and expensive elastic materials in an effort to control the pressures and flow rates.
Recent developments as disclosed in U.S. Pat. No. 5,080,652 entitled Infusion Apparatus issued to Sancoif et al, and U.S. Pat. No. 5,105,983 entitled Infusion Apparatus issued Apr. 21, 1992 to Sancoif et al and assigned to the Assignee hereof have overcome many of the problems of the prior art. However, these have some drawbacks, namely they are undesirably bulky for some applications.
It is desirable that an improved infusion device be available that overcomes the above problems of the prior art. More specifically it is desirable that a compact infusion device be available wherein the pressure and flow rate are reasonably constant over the infusion period.